Odd patina effect

[davepl]

This is from the recent patina thread, but has me confused.

But look at the tailgate and how the "CHEVROLET" letters appear to cast a drop shadow. If it were from the top down I could see it being from the shadow of the letters, but the angle isn't right for strong sun.

I thought perhaps when the truck was originally sprayed the raised portions created a shadow where there was less paint and hence faster rust, except the 'shadow' from the T has more rust and the shadow from the handle has less. If it were a result of the direction of the gun when it was first painted, you'd expect less paint in the 'shadow' of the letters, and hence more rust. That's what we see. Except the tailgate handle is the opposite, which is confusing.

Any good theories?